1. Field of the Invention
The present invention relates to an electronic control apparatus having a supervisory control circuit, which is applicable to a vehicle mounted engine control system, etc., and in particular to an improved technique of an electronic control apparatus which has an inexpensive supervisory control circuit part of a medium speed operation connected in series to a main control circuit part that is provided with a microprocessor of high performance operating at high speed.
2. Description of the Related Art
In the past, as an electronic control apparatus having a supervisory control circuit, there has been proposed a technique in which a supervisory control circuit part is formed to be mutually connected in series to a main control circuit part composed of a microprocessor so as to mutually supervise their operations (for example, see a first patent document).
In the conventional apparatus described in the above-mentioned first patent document, it is constructed such that the supervisory control circuit part transmits through reference packets a lot of questionnaires in a sequential manner to the microprocessor, which constitutes the main control circuit part and performs an input and output control operation, and makes an abnormality determination with respect to the control operation of the microprocessor by making a comparison between the content of a response from the microprocessor and the correct answer information beforehand stored at a supervisory control circuit side, and the microprocessor reversely supervises the supervisory operation of the supervisory control circuit part by diagnosing the receiving interval of the reference packets.
Here, note that in cases where the supervisory control circuit part is operated by frequency dividing a highly precise clock signal used in the main control circuit part, there is a problem that when this clock signal becomes abnormal, both the main control circuit part and the supervisory control circuit part also become abnormal at the same time, so it is desirable to use an inexpensive oscillator, independently of the main control circuit part, as an oscillator for the clock signal by means of which the supervisory control circuit part is driven to operate.
On the other hand, in the past, there has also been proposed a vehicle mounted electronic control apparatus which corrects the period or cycle of a clock signal of low precision used in a supervisory control circuit part by the use of a highly precise reference clock signal supplied from a main control circuit part (for example, see a second patent document).
In the vehicle mounted electronic control apparatus described in the above-mentioned second patent document, there is disclosed a technique which is provided with an awakening control circuit part (corresponding to the supervisory control circuit part) that is connected in series to a microprocessor forming the main control circuit part, wherein the operating cycle of the clock signal of low precision used in the awakening control circuit part is corrected by the highly precise reference clock signal that is obtained by performing frequency division of the highly precise clock signal which is operating at high speed and is used in the main control circuit part, and the time elapsed after the operation of the main control circuit part is stopped is measured by the awakening control circuit part, so that the main control circuit part is reactivated or restarted after a predetermined period of time.